NATURE 



409 



THURSDAY, MARCH 5, 1896. 



THEORIES OF EVOLUTION. 

 Darwin and After Danvin : an Exposition oj the 

 Darwinian Theory^ and a Discussion of Post- Dar- 

 winian (Juestions. By the late G. J. Romanes, F.R.S. 

 &c. II. Post-Darwinian Questions — Heredity and 

 Utility. Pp. 344. (London : Longmans, Green, and 

 Co., 1895.) 

 pROF. LLOYD MORGAN tells us, in a prefatory 

 ^ note, that the greater part of this work was in type 

 before the lamented death of the author. The material 

 for chapters v. and vi. existed in the form of " notes and 

 isolated paragraphs," which have been arranged for the 

 press, but otherwise practically untouched. The editor 

 has performed his task with great skill, and has succeeded 

 in attaining the object which he wisely held in view^ — 

 the production of a work which is in every way charac- 

 teristic of its author and of no one else. 



The frontispiece is an admirable reproduction of a 

 photograph of the author — a most excellent likeness, 

 which will, in itself, invest the book with deep interest 

 for many readers. 



Of the ten chapters, the first is introductory, the suc- 

 ceeding five deal with " characters as hereditary and 

 acquired," while the remaining four are devoted to 

 " characters as adaptive and specific." 



In the introductory chapter, the views of Darwin and 

 Wallace are contrasted in much detail. In a table on 

 p. 6, "the theory of Natural Selection according to 

 Darwin" is apparently compared with "the theory of 

 Natural Selection according to Wallace": in reality, 

 however, the theories are not compared or contrasted in 

 any way — the only comparison being in the extent to 

 which they were applied by these two naturalists 

 respectively, and in their use or neglect of accessory 

 theories. The high importance which Wallace ascribes 

 to natural selection, and his inability to accept any other 

 existing suggestions as to the origin of species, are, in 

 this table, brought together into a set of dogmatic state- 

 ments, which, as the present writer thinks, are far from 

 expressing his views. 



It is contended that Darwin progressively ascribed less 

 and less importance to natural selection : " The longer 

 he lived, and the more he pondered these points, the less 

 exclusive was the ro/c which he assigned to natural 

 selection, and the more importance did he attribute to the 

 supplementary factors " (p. 8 ; see also p. 40). Some of 

 his latest letters, however, do not support this view of an 

 unbroken progressive tendency. 



Many of the authors well-known arguments against 

 the use of the term " Darwinism," as opposed to 

 " Lamarckism," are here reproduced and brought forward 

 in a very forcible manner. The contest, however, is 

 entirely due to the fact that the combatants ascribe 

 diflferent meanings to the same word. To the author, 

 " Darwinism " means the whole of the views which 

 Darwin entertained upon the origin of species ; to his 

 opponents, " Darwinism " means those views upon this 

 subject which were originated by Darwin (viz. the theory 

 of natural selection). It is no doubt true, as is contended 

 NO. 1375, VOL. 53] 



on pp. 10, II, that the " Lamarckian " principles (of use 

 and disuse, &c.) accepted by Darwin were independently 

 conceived by him, and that he did not owe them to 

 Lamarck ; but the fact remains that they were originated 

 by the latter, and not by Darwin. 



The latter part of the introductory chapter deals in a 

 brief but very effective manner with the three theories of 

 evolution associated with the names of Cope, Geddes, and 

 Henslow, and in greater detail with Wallace's well-known 

 views upon the insufficiency of natural selection to 

 account for the origin of the human race. 



In chapter ii. the relationship between W^eismann's 

 views is represented in the diagram on p. 43, and in 

 statements which describe the formation of a " postulate 

 as to the absolute non-inheritance of acquired characters" 

 in order to support the "deduction as to the absolute con- 

 tinuity of germ-plasm," and this again in order to support 

 the further deductions " as to the theory of organic 

 evolution" and "as to the architecture of germ-plasm." 

 From this mode of representation the reader unacquainted 

 with Weismann's writings, at first hand, might readily re- 

 ceive the impression of a flimsy speculative structure 

 unsupported by investigation, which would be doing 

 scant justice to the distinguished German biologist. 



W^eismann's theory of heredity, based on the continuity 

 of the germ-plasm, grew directly out of his researches 

 upon the sexual cells of Hydrozoa, and was thus founded 

 directly upon the results of investigation. The hereditary 

 transmission of acquired characters was not at first called 

 into question, but, later on, the extreme difficulty of ex- 

 plaining such transmission by means of a theory of 

 heredity, which on other grounds appeared to be sound, 

 suggested an inquiry into the supposed fact of the trans- 

 mission itself This subject was then dealt with on its 

 own merits, and it was soon apparent that the evidence 

 had a very different bearing^from that which had been 

 generally assumed. The later and frequently changing 

 hypotheses as to the architecture of the germ-plasm were 

 an attempt to explain the results of the unceasing inquiry 

 into the changes undergone by the sexual cells. Ne\ver 

 and more complex phases of change were ever being 

 made out in this most fruitful field of investigation, sug- 

 gesting modifications in the details of Weismann's hypo- 

 thesis of the structure of germ-plasm, and not ending 

 here, but suggesting also fresh lines of observation and 

 research. Indeed it may be maintained that the errors 

 which have appeared from time to time in the details of 

 Weismann's hypotheses are due to an attempt to render 

 the hypotheses too much up-to-date, by taking into 

 account all the most recent observations in an excep- 

 tionally difficult line of research— observations many of 

 which could not be final, and some of which were bound 

 to be altogether erroneous. 



It will be impossible to attempt any adequate dis- 

 cussion of the admirable treatment of the facts and 

 arguments for and against the hereditary transmission 

 of acquired characters. These chapters will require the 

 careful consideration of writers on either side of the 

 controversy. Not only is the discussion itself most 

 valuable, but new facts are submitted. Brown-Sequard's 

 experiments on guinea-pigs have been repeated with 

 great care, but no definite conclusions can be safely 

 drawn from the results. " On the w hole, then, as regards 



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